expression

This section is different from the others. Most other sections of
this document talks about a particular SQL command. This section does
not talk about a standalone command but about "expressions" which are
subcomponents of most other commands.

Operators

SQLite understands the following binary operators, in order from
highest to lowest precedence:

The COLLATE operator is a unary postfix
operator that assigns a collating sequence to an expression.
The COLLATE operator has a higher precedence (binds more tightly) than any
binary operator and any unary prefix operator except "~".
(COLLATE and "~" are associative so their binding order does not matter.)
The collating sequence set by the COLLATE operator overrides the
collating sequence determined by the COLLATE clause in a table
column definition.
See the detailed discussion on collating sequences
in the Datatype In SQLite3 document for additional information.

The unary operator + is a no-op. It can be applied
to strings, numbers, blobs or NULL and it always returns a result
with the same value as the operand.

Note that there are two variations of the equals and not equals
operators. Equals can be either
= or ==.
The non-equals operator can be either
!= or <>.
The || operator is "concatenate" - it joins together
the two strings of its operands.
The operator % outputs the value of its left
operand modulo its right operand.

The result of any binary operator is either a numeric value or
NULL, except for the || concatenation operator which always
evaluates to either NULL or a text value.

The IS and IS NOT operators work
like = and != except when one or both of the
operands are NULL. In this case, if both operands are NULL, then the
IS operator evaluates to 1 (true) and the IS NOT operator evaluates
to 0 (false). If one operand is NULL and the other is not, then the
IS operator evaluates to 0 (false) and the IS NOT operator is 1 (true).
It is not possible for an IS or IS NOT expression to evaluate to NULL.
Operators IS and IS NOT have the same
precedence as =.

Literal Values (Constants)

A literal value represents a constant.
Literal values may be integers, floating point numbers, strings,
BLOBs, or NULLs.

The syntax for integer and floating point literals (collectively
"numeric literals") is shown by the following diagram:

If a numeric literal has a decimal point or an exponentiation
clause or if its magnitude is less than -9223372036854775808 or
greater than 9223372036854775807, then it is a floating point literal.
Otherwise is it is an integer literal.
The "E" character that begins the exponentiation
clause of a floating point literal can be either upper or lower case.
The "." character is always used
as the decimal point even if the locale setting specifies "," for
this role - the use of "," for the decimal point would result in
syntactic ambiguity.

Hexadecimal integer literals follow the C-language notation of
"0x" or "0X" followed by hexadecimal digits.
For example, 0x1234 means the same as 4660
and 0x8000000000000000 means the same as -9223372036854775808.
Hexadecimal integer literals are interpreted as 64-bit
two's-complement integers and are thus limited
to sixteen significant digits of precision.
Support for hexadecimal integers was added to SQLite
version 3.8.6 (2014-08-15).
For backwards compatibility, the "0x" hexadecimal integer
notation is only understood by the SQL language parser, not by the
type conversions routines.
String variables that
contain text formatted like hexadecimal integers are not
interpreted as hexadecimal integers when coercing the string value
into an integer due to a CAST expression or for a column affinity
transformation or prior to performing a numeric operation or for
any other run-time conversions. When coercing a
string value in the format of a hexadecimal integer into an integer
value, the conversion process stops when the 'x' character is seen
so the resulting integer value is always zero.
SQLite only understands the hexadecimal integer notation when it
appears in the SQL statement text, not when it appears as
part of the content of the database.

A string constant is formed by enclosing the
string in single quotes ('). A single quote within the string can
be encoded by putting two single quotes in a row - as in Pascal.
C-style escapes using the backslash character are not supported because
they are not standard SQL.

BLOB literals are string literals containing hexadecimal data and
preceded by a single "x" or "X" character. Example: X'53514C697465'

A literal value can also be the token "NULL".

Parameters

A "variable" or "parameter" token
specifies a placeholder in the expression for a
value that is filled in at runtime using the
sqlite3_bind() family of C/C++ interfaces.
Parameters can take several forms:

?NNN

A question mark followed by a number NNN holds a spot for the
NNN-th parameter. NNN must be between 1 and SQLITE_MAX_VARIABLE_NUMBER.

?

A question mark that is not followed by a number creates a parameter
with a number one greater than the largest parameter number already assigned.
If this means the parameter number is greater than
SQLITE_MAX_VARIABLE_NUMBER, it is an error.
This parameter format is provided for compatibility with other database
engines. But because it is easy to miscount the question marks, the
use of this parameter format is discouraged. Programmers are encouraged
to use one of the symbolic formats below or the ?NNN format above instead.

:AAAA

A colon followed by an identifier name holds a spot for a
named parameter with the name :AAAA.
Named parameters are also numbered. The number assigned is one greater than
the largest parameter number already assigned. If this means the parameter
would be assigned a number greater than SQLITE_MAX_VARIABLE_NUMBER, it is
an error. To avoid confusion, it is best to avoid mixing named and numbered
parameters.

@AAAA

An "at" sign works exactly like a colon, except that the name of
the parameter created is @AAAA.

$AAAA

A dollar-sign followed by an identifier name also holds a spot for a named
parameter with the name $AAAA. The identifier name in this case can include
one or more occurrences of "::" and a suffix enclosed in "(...)" containing
any text at all. This syntax is the form of a variable name in the
Tcl programming language. The presence
of this syntax results from the fact that SQLite is really a
Tcl extension that has escaped into the wild.

The LIKE, GLOB, REGEXP, and MATCH operators

The LIKE operator does a pattern matching comparison. The operand
to the right of the LIKE operator contains the pattern and the left hand
operand contains the string to match against the pattern.
A percent symbol ("%") in the LIKE pattern matches any
sequence of zero or more characters in the string. An underscore
("_") in the LIKE pattern matches any single character in the
string. Any other character matches itself or its lower/upper case
equivalent (i.e. case-insensitive matching).
Important Note: SQLite only
understands upper/lower case for ASCII characters by default. The
LIKE operator is case sensitive by default for unicode characters that are
beyond the ASCII range. For example,
the expression 'a' LIKE 'A'
is TRUE but 'æ' LIKE 'Æ' is FALSE.
The ICU extension to SQLite includes an enhanced version of the
LIKE operator that does case folding across all unicode characters.

If the optional ESCAPE clause is present, then the expression
following the ESCAPE keyword must evaluate to a string consisting of
a single character. This character may be used in the LIKE pattern
to include literal percent or underscore characters. The escape
character followed by a percent symbol (%), underscore (_), or a second
instance of the escape character itself matches a
literal percent symbol, underscore, or a single escape character,
respectively.

The infix LIKE operator is implemented by calling the
application-defined SQL functions like(Y,X) or
like(Y,X,Z).

The GLOB operator is similar to LIKE but uses the Unix
file globbing syntax for its wildcards. Also, GLOB is case
sensitive, unlike LIKE. Both GLOB and LIKE may be preceded by
the NOT keyword to invert the sense of the test. The infix GLOB
operator is implemented by calling the function
glob(Y,X) and can be modified by overriding
that function.

The REGEXP operator is a special syntax for the regexp()
user function. No regexp() user function is defined by default
and so use of the REGEXP operator will normally result in an
error message. If an application-defined SQL function named "regexp"
is added at run-time, then the "X REGEXP Y" operator will
be implemented as a call to "regexp(Y,X)".

The MATCH operator is a special syntax for the match()
application-defined function. The default match() function implementation
raises an exception and is not really useful for anything.
But extensions can override the match() function with more
helpful logic.

The BETWEEN operator

The BETWEEN operator is logically equivalent to a pair of comparisons.
"xBETWEENyANDz" is
equivalent to
"x>=yANDx<=z" except
that with BETWEEN, the x expression is only evaluated once.
The precedence of the BETWEEN operator is the same as the precedence
as operators == and != and LIKE and groups left to right.

The CASE expression

A CASE expression serves a role similar to IF-THEN-ELSE in other
programming languages.

The optional expression that occurs in between the CASE keyword and the
first WHEN keyword is called the "base" expression. There are two basic forms
of the CASE expression: those with a base expression and those without.

In a CASE without a base expression, each WHEN expression is evaluated
and the result treated as a boolean, starting with the leftmost and continuing
to the right. The result of the CASE expression is the evaluation of the THEN
expression that corresponds to the first WHEN expression that evaluates to
true. Or, if none of the WHEN expressions evaluate to true, the result of
evaluating the ELSE expression, if any. If there is no ELSE expression and
none of the WHEN expressions are true, then the overall result is NULL.

A NULL result is considered untrue when evaluating WHEN terms.

In a CASE with a base expression, the base expression is evaluated just
once and the result is compared against the evaluation of each WHEN
expression from left to right. The result of the CASE expression is the
evaluation of the THEN expression that corresponds to the first WHEN
expression for which the comparison is true. Or, if none of the WHEN
expressions evaluate to a value equal to the base expression, the result
of evaluating the ELSE expression, if any. If there is no ELSE expression and
none of the WHEN expressions produce a result equal to the base expression,
the overall result is NULL.

When comparing a base expression against a WHEN expression, the same
collating sequence, affinity, and NULL-handling rules apply as if the
base expression and WHEN expression are respectively the left- and
right-hand operands of an = operator.

If the base
expression is NULL then the result of the CASE is always the result
of evaluating the ELSE expression if it exists, or NULL if it does not.

Both forms of the CASE expression use lazy, or short-circuit,
evaluation.

The only difference between the following two CASE expressions is that
the x expression is evaluated exactly once in the first example but
might be evaluated multiple times in the second:

CASE x WHEN w1 THEN r1 WHEN w2 THEN r2 ELSE r3 END

CASE WHEN x=w1 THEN r1 WHEN x=w2 THEN r2 ELSE r3 END

The IN and NOT IN operators

The IN and NOT IN operators take a single scalar operand on the
left and a vector operand on the right
formed by an explicit list of zero or more scalars or by a
single subquery.
When the right operand of an IN or NOT IN operator is a subquery, the
subquery must have a single result column.
The "subquery" on the right-hand side of an IN operator can be a
table name or table-valued function name in which case the
subquery is understood to be "(SELECT * FROM name)".
When the right operand is an empty set, the result of IN is false and the
result of NOT IN is true, regardless of the left operand and even if the
left operand is NULL.

The result of an IN or NOT IN operator is determined by the following
matrix:

Left operand is NULL

Right operand contains NULL

Right operand is an empty set

Left operand found within right operand

Result of IN operator

Result of NOT IN operator

no

no

no

no

false

true

does not matter

no

yes

no

false

true

no

does not matter

no

yes

true

false

no

yes

no

no

NULL

NULL

yes

does not matter

no

does not matter

NULL

NULL

Note that SQLite allows the parenthesized list of scalar values on
the right-hand side of an IN or NOT IN operator to be an empty list but
most other SQL database database engines and the SQL92 standard require
the list to contain at least one element.

The EXISTS operator

The EXISTS operator always evaluates to one of the integer values 0
and 1. If executing the SELECT statement specified as the right-hand
operand of the EXISTS operator would return one or more rows, then the
EXISTS operator evaluates to 1. If executing the SELECT would return
no rows at all, then the EXISTS operator evaluates to 0.

The number of columns in each row returned by the SELECT statement
(if any) and the specific values returned have no effect on the results
of the EXISTS operator. In particular, rows containing NULL values are
not handled any differently from rows without NULL values.

Scalar Subqueries

A SELECT statement enclosed in parentheses may appear as a scalar
quantity. A SELECT used as a scalar quantity must return a result set
with a single column. The result of the expression is the value of the
only column in the first row returned by the SELECT statement. If the SELECT
yields more than one result row, all rows after the first are ignored. If
the SELECT yields no rows, then the value of the expression is NULL.
The LIMIT of a scalar subquery is always 1.
Any other LIMIT value given in the SQL text is ignored.

All types of SELECT statement, including aggregate and compound SELECT
queries (queries with keywords like UNION or EXCEPT) are allowed as scalar
subqueries.

Table Column Names

A column name can be any of the names defined in the CREATE TABLE
statement or one of the following special identifiers: "ROWID",
"OID", or "_ROWID_".
The three special identifiers describe the
unique integer key (the rowid) associated with every
row of every table and so are not available on WITHOUT ROWID tables.
The special identifiers only refer to the row key if the CREATE TABLE
statement does not define a real column with the same name.
The rowid can be used anywhere a regular
column can be used.

Correlated Subqueries

A SELECT statement used as either a scalar subquery or as the
right-hand operand of an IN, NOT IN or EXISTS expression may contain
references to columns in the outer query. Such a subquery is known as
a correlated subquery. A correlated subquery is reevaluated each time
its result is required. An uncorrelated subquery is evaluated only once
and the result reused as necessary.

CAST expressions

A CAST expression of the form "CAST(expr AS type-name)"
is used to convert the value of expr to
a different storage class specified by type-name.
A CAST conversion is similar to the conversion that takes
place when a column affinity is applied to a value except that with
the CAST operator the conversion always takes place even if the conversion
lossy and irreversible, whereas column affinity only changes the data type
of a value if the change is lossless and reversible.

If the value of expr is NULL, then the result of the CAST
expression is also NULL. Otherwise, the storage class of the result
is determined by applying the rules for determining column affinity to
the type-name.

Affinity of type-name

Conversion Processing

NONE

Casting a value to a type-name with no affinity
causes the value to
be converted into a BLOB. Casting to a BLOB consists of first casting
the value to TEXT in the encoding of the database connection, then
interpreting the resulting byte sequence as a BLOB instead of as TEXT.

TEXT

To cast a BLOB value to TEXT, the sequence of bytes that make up the
BLOB is interpreted as text encoded using the database encoding.

Casting an INTEGER or REAL value into TEXT renders the value as if via
sqlite3_snprintf() except that the resulting TEXT uses the encoding of
the database connection.

REAL

When casting a BLOB value to a REAL, the value is first converted to
TEXT.

When casting a TEXT value to REAL, the longest possible prefix of
the value that can be interpreted as a real number is extracted from
the TEXT value and the remainder ignored. Any leading spaces in the
TEXT value are ignored when converging from TEXT to REAL. If there is
no prefix that can be interpreted as a real number, the result of the
conversion is 0.0.

INTEGER

When casting a BLOB value to INTEGER, the value is first converted to
TEXT.

When casting a TEXT value to INTEGER, the longest possible prefix of
the value that can be interpreted as an integer number is extracted from
the TEXT value and the remainder ignored. Any leading spaces in the
TEXT value when converting from TEXT to INTEGER are ignored. If there
is no prefix that can be interpreted as an integer number, the result
of the conversion is 0. The CAST operator understands decimal
integers only — conversion of hexadecimal integers stops
at the "x" in the "0x" prefix of the hexadecimal integer string
and thus result of the CAST is always zero.

A cast of a REAL value into an INTEGER results in the integer
between the REAL value and zero that is closest to the REAL value.
If a REAL is greater than the greatest possible signed
integer (+9223372036854775807) then the result is the greatest possible
signed integer and if the REAL is less than the least possible signed
integer (-9223372036854775808) then the result is the least possible
signed integer.

Prior to SQLite version 3.8.2 (2013-12-06),
casting a REAL value greater than
+9223372036854775807.0 into an integer resulted in the most negative
integer, -9223372036854775808. This behavior was meant to emulate the
behavior of x86/x64 hardware when doing the equivalent cast.

NUMERIC

Casting a TEXT or BLOB value into NUMERIC first does a forced
conversion into REAL but then further converts the result into INTEGER if
and only if the conversion from REAL to INTEGER is lossless and reversible.
This is the only context in SQLite where the NUMERIC and INTEGER affinities
behave differently.

Casting a REAL or INTEGER value to NUMERIC is a no-op, even if a real
value could be losslessly converted to an integer.

Note that the result from casting any non-BLOB value into a
BLOB and the result from casting any BLOB value into a non-BLOB value
may be different depending on whether the database encoding is UTF-8,
UTF-16be, or UTF-16le.

Boolean Expressions

The SQL language features several contexts where an expression is
evaluated and the result converted to a boolean (true or false) value. These
contexts are:

the WHERE clause of a SELECT, UPDATE or DELETE statement,

the ON or USING clause of a join in a SELECT statement,

the HAVING clause of a SELECT statement,

the WHEN clause of an SQL trigger, and

the WHEN clause or clauses of some CASE expressions.

To convert the results of an SQL expression to a boolean value, SQLite
first casts the result to a NUMERIC value in the same way as a
CAST expression. A numeric zero value (integer value 0 or real
value 0.0) is considered to be false. A NULL value is still NULL.
All other values are considered true.

For example, the values NULL, 0.0, 0, 'english' and '0' are all considered
to be false. Values 1, 1.0, 0.1, -0.1 and '1english' are considered to
be true.

It is possible to have an aggregate function with the same name as a
simple function, as long as the number of arguments for the two forms of the
function are different. For example, the max() function with a
single argument is an aggregate and the max() function with two or more
arguments is a simple function.